U.S. Pat. No. 4,762,516 (Luther et al.) and U.S. patent application Ser. No. 335,472, filed Apr. 10, 1989, describe I.V. catheters with needle guards that are designed to protect medical personnel from inadvertent injury caused by needle sticks subsequent to use of the catheter needle. Such inadvertent needle sticks can result in infection by diseases borne by the blood of the patient from whose vascular system the needle has been previously withdrawn. The catheters described in this patent and patent application prevent inadvertent needle sticks by covering the needle tip with a needle guard extending from the needle hub as the needle is withdrawn from the patient's body.
It is not only desirable to protect medical personnel from the hazards of inadvertent needle sticks, but it is further desirable to provide protection from any contact with a patient's blood. Even in the use of one of the aforementioned catheters with needle guards, it is possible for medical personnel to come into contact with a patient's blood due to undesired leakage of blood from the catheter. During insertion of the needle into the vascular system of the patient, the clinician administering the catheter will try to locate the tip of the needle in a vein or artery of the patient. When the needle tip is properly located, there will be a small flow or flash of blood through the hollow needle and into the flash chamber at the proximal end of the needle. The clinician will note this presence of blood in the flash chamber as an indication of proper needle placement. The clinician can then advance the catheter into the vascular system and withdraw the needle from the patient, leaving the catheter cannula in place in the blood vessel.
As the needle tip moves to a location proximal the distal end of the catheter, blood will flow under venous or arterial pressure into the catheter and into the hollow needle. However blood may also enter the annular space between the outer wall of the needle and the inner wall of the catheter cannula. The flow of blood in this space toward the catheter hub is herein referred to as backflow. Normally, backflow of blood is of little concern, because the catheter hub is usually quickly connected to a tubing set once the needle is withdrawn from the catheter. However, in the aforementioned catheters with needle guards, the distal nose of the needle guard occupies the catheter hub prior to complete withdrawal of the needle. As the needle guard is extended along the length of the needle toward the needle tip, its extension will carry the catheter hub to simultaneously thread the catheter into the vein or artery of the patient. The termination of this motion will eject the catheter hub from the nose of the guard when the guard reaches it full extention. Thus, if blood backflow into the catheter hub occurs prior to ejection of the catheter hub from the nose of the guard, the needle guard will be contaminated with the patient's blood prior to the release of the catheter hub. It would be desirable to prevent this contamination so that contact by medical personnel with blood on the nose of the needle guard will be prevented.
One technique for deterring blood backflow into the catheter hub is described in U.S. patent application Ser. No. 353,276, filed May 17, 1989. This technique involves the formation of a restriction by the narrowing of the inner diameter of a proximal portion of the catheter tube. The restriction causes that portion of the catheter tube to fit closely around the insertion needle, substantially deterring the flow of blood through the restriction about the needle. Only a very small amount of blood is able to pass through the restriction and flow into the catheter hub prior to withdrawal of the needle from the catheter tube.
However, once the needle is withdrawn to a position proximal the restriction, there is no impediment to blood flowing into the catheter hub and around the nose of the needle guard located inside the hub. Even though this condition is only a momentary one before the needle guard is removed from the catheter hub and the hub is connected to a tubing set, it remains desirable to deter any blood backflow both prior to and at this time. This is because blood flowing into the catheter hub may still pass through the aperture of the needle guard nose through which the needle extends. Blood backflow through the aperture of the needle guard can exit the rear of the needle guard and coat the needle, where it can inadvertently come into contact with the clinician who is inserting the catheter and removing the needle assembly. Hence, it remains desirable to prevent blood backflow through the aperture at the nose of the needle guard through which the needle passes.